This invention relates to isomerization of alkenes and more particularly relates to selective low-temperature isomerization of normal butenes using a catalyst containing hydrogen form AMS-1B crystalline molecular sieve.
Normal butenes, such as 1-butene and 2-butenes, are common refinery products which are used especially in alkylation of isobutane to form gasoline-fraction hydrocarbons. Approximately fifty percent of refinery-produced normal butenes is 1-butene. Since 2-butenes, i.e., cis-2-butene and trans-2-butene, produce an alkylate with a higher octane number than alkylate produced from 1-butene, a process to convert 1-butene to 2-butenes would be desirable. Catalyst systems have been developed for this conversion. However, there is a need for a reliable catalyst system which can be regenerated easily such as based on molecular sieves.
Zeolitic materials, both natural and synthetic, are known to have catalytic capabilities for many hydrocarbon processes. Zeolitic materials typically are ordered, porous crystalline aluminosilicates having a definite structure with cavities interconnected by channels. The cavities and channels throughout the crystalline material generally are uniform in size allowing selective separation of hydrocarbons. Consequently, these materials in many instances are known in the art as "molecular sieves" and are used, in addition to selective adsorptive processes, for certain catalytic properties. The catalytic properties of these materials are affected to some extent by the size of the molecules which selectively penetrate the crystal structure, presumably to contact active catalytic sites within the ordered structure of these materials.
Generally, the term "molecular sieve" includes a wide variety of both natural and synthetic positive-ion-containing crystalline zeolite materials. They generally are characterized as crystalline alumino-silicates which comprise networks of SiO.sub.4 and AlO.sub.4 tetrahedra in which silicon and aluminum atoms are cross-linked by sharing of oxygen atoms. The negative framework charge resulting from substitution of an aluminum atom for a silicon atom is balanced by positive ions, for example, alkali-metal or alkaline-earth-metal cations, ammonium ions, or hydrogen ions.
Prior art developments have resulted in formation of many synthetic zeolitic crystalline materials. Crystalline aluminosilicates are the most prevalent and, as described in the patent literature and in the published journals, are designated by letters or other convenient symbols. Examples of these materials are Zeolite A (U.S. Pat. No. 2,882,243), Zeolite X (U.S. Pat. No. 2,882,244), Zeolite Y (U.S. Pat. No. 3,130,007), Zeolite ZSM-4 (U.S. Pat. No. 3,578,723), Zeolite ZSM-5 (U.S. Pat. No. 3,702,886), Zeolite ZSM-11 (U.S. Pat. No. 3,709,979), Zeolite ZSM-12 (U.S. Pat. No. 3,832,449), Zeolite NU-1 (U.S. Pat. No. 4,060,590) and others.
Boron is not considered a replacement for aluminum or silicon in a zeolitic composition. However, recently a new crystalline borosilicate molecular sieve AMS-1B with distinctive properties was disclosed in U.S. Pat. Nos. 4,268,420, 4,269,813 and 4,285,919 incorporated by reference herein. According to these patents AMS-1B can be synthesized by crystallizing a source of an oxide of silicon, an oxide of boron, an oxide of sodium and an organic template compound such as a tetra-n-propylammonium salt. The process of this invention uses AMS-1B crystalline borosilicate molecular sieve.
Hydrocarbon conversion processes are known using other zeolitic materials. Examples of such processes are dewaxing of oil stock (U.S. Pat. Nos. 3,852,189, 4,211,635 and reissue U.S. Pat. No. Re. 28,398); conversion of lower olefins (U.S. Pat. Nos. 3,965,205 and 3,960,978, and European patent application No. 31,675); aromatization of olefins and aliphatics (U.S. Pat. Nos. 3,761,389, 3,813,330, 3,827,867, 3,827,868, 3,843,740, 3,843,741 and 3,914,171); hydrocracking and oligomerization of hydrocarbons (U.S. Pat. Nos. 3,753,891, 3,767,568, 3,770,614 and 4,032,432); conversion of ethane to aromatics and C.sub.3.sup.+ hydrocarbons (U.S. Pat. No. 4,100,218); conversion of straight-chain and slightly branched chain hydrocarbons to olefins (U.S. Pat. Nos. 4,309,275 and 4,309,276); and conversion of C.sub.4 paraffins to aromatics (U.S. Pat. No. 4,291,182).
Conversion of C.sub.4 hydrocarbons using AMS-1B crystalline borosilicate under some conditions is described in commonly assigned U.S. patent applications Ser. No. 422,743 in the name of Peters and Klotz, Ser. No. 422,742 in the name of Sikkenga, Ser. No. 422,821 in the name of Nevitt, Sikkenga, and Jerome and Ser. No. 422,744 in the name of Nevitt and Jerome, all filed of even date herewith and all incorporated by reference herein.
The improvement described herein is the discovery that use of a catalyst formulation containing AMS-1B crystalline borosilicate molecular sieve at low conversion temperatures below 250.degree. C. selectively converts a 1-alkene, such as 1-butene, to 2-alkenes, such as 2-butenes.
A method to isomerize normal butenes such as n-butenes would be desirable and a method that would isomerize a 1-alkene to 2-alkenes without excessive losses to undesirable by-products would be especially desirable. Further, a process that converts 1-butene to more useful and valuable products such as cis-2-butene and trans-2-butene would be very advantageous.